This invention relates to laminated ceramic devices and more particularly to methods of laminating the ceramic devices.
At the present time, and especially in the RF field, many electronic components are formed on or in ceramic modules. In the process of forming the ceramic modules, thin sheets of unfired or xe2x80x9cgreenxe2x80x9d ceramic material are provided which, as is known in the art, usually includes Al2O3 particles, glass particles, and a binder, generally including organic material. Each sheet generally includes a plurality of module layers formed adjacent each other so as to share sides. Each module layer on the sheet generally includes some electrical traces and may further include some electrical components such as capacitors, inductors, resistors, etc. Each module layer also includes vias extending therethrough. Components and electrical traces may be formed on the sheets by screening (or the like) silver paint or other conductive material.
A plurality of the sheets (sometimes as many as fifty) are stacked or positioned in overlying relationship and vertically aligned to form common module sides through the entire stack. It will of course be understood that internal vias and various other connections are also aligned during this process to provide one or more complete interconnected circuits in each of the modules.
After the stacking and alignment of the sheets is accomplished, the stack is pressed under a uniaxial pressure at an elevated temperature to produce bonding between adjacent sheets. Generally, the temperature is elevated to approximately 70xc2x0 C. and a pressure of approximately 5000 pounds-per-square-inch (psi) is applied. As understood by those skilled in the art, the pressure and temperature must be sufficient to produce some bonding between the binders of adjacent sheets. If adequate binding does not occur, the sheets may be inadvertently separated during subsequent handling, resulting in destruction of the entire assembly.
Once the stack of unfired or green ceramic sheets has been assembled and the individual sheets bonded together, the stack is cut or otherwise divided into individual modules. Generally, for example, the stack is cut with a very sharp instrument. The cutting is easily accomplished since the sheets are still formed of unfired or green ceramic. Again, if the stack is not adequately bonded, the sheets may be inadvertently separated during the cutting operation.
One major problem that occurs with this prior art process of forming ceramic modules is the amount of pressure that must be applied to achieve adequate bonding of the unfired ceramic sheets. Internal cavities and channels cannot be incorporated, for example, because this high pressure causes deformations in this type of feature. Also, this prior process is slow and cannot be easily implemented within an automated production line (i.e. the automated multilayer manufacturing stages are separated by the high-pressure lamination process which is inherently a high labor technology).
Accordingly it is highly desirable to provide new and improved methods of forming intermediate low-pressure laminated ceramic devices and new laminated ceramic devices that can easily be formed with internal cavities and channels.